Patent GB-834148-A (GB)
Title: Process of treating titanium, zirconium of hafnium or their alloys
IPC: C23F1/14
Filed: 1958-01-01
Abstract: Titanium, zirconium, hafnium and their alloys are dissolved in a solution of ammonium fluoride, e.g. of pH 5 to 8, preferably in a concentration of 5 to 50%, and at a temperature of 20 DEG  to 150 DEG C. in order to remove surface contaminants such as oxides and nitrides, to chemically reduce the size of a piece of the metal or to dissolve the metal prior to the preparation of compounds thereof.  An example describes the recovery of a zirconium alloy from lathe turnings from an ingot having a hardness of 189 BHN.  A sample of the degreased turnings when melted in an arc furnace yielded an ingot having a hardness of 207 BHN.  Three separate batches of degreased turnings were immersed in a neutral solution of 30% ammonium fluoride and left long enough for 6% by weight of the metal to be removed after which the turnings were washed in 5% nitric acid, water acetone and then dried.  The ingots resulting from arc-melting the samples had hardnesses of 181, 185 and 185 respectively.  The ammonium metal fluoride in solution may be hydrolysed to the hydrated metal oxide by the addition of ammonia solution, the former being removed by filtration and ammonium fluoride being recovered from the filtrate, or the ammonium fluoride concentration of the solution of ammonium metal fluoride may be increased and the resultant crystals of the ammonium metal fluoride separated by filtration and ammonium fluoride recovered from the filtrate.  Chemical machining may be accomplished by masking the metal article, except for the area to be removed, with a protective coating after which the article is immersed and the unprotected areas dissolved at a controlled rate in neutral ammonium fluoride solution.ALSO:Titanium, zirconium, hafnium and their alloys are dissolved in a solution of ammonium fluoride, e.g. of pH 5 to 8 preferably in a concentration of 5 to 50% and at a temperature of 20 to 150 DEG C. in order to remove surface contaminants such as oxides and nitrides, to chemically reduce the size of a piece of the metal or to dissolve the metal prior to the preparation of compounds thereof.  An example describes the recovery of a zirconium alloy from lathe turnings from an ingot having a hardness of 189 BHN.  A sample of the degreased turnings when melted in an arc furnace yielded an ingot having a hardness of 207 BHN.  Three separate batches of degreased turnings were immersed in a neutral solution of 30% ammonium fluoride and left long enough for 6% by weight of the metal to be removed after which the turnings were washed in 5% nitric acid, water acetone and then dried.  The ingots resulting from arc-melting the samples had hardnesses of 181, 185 and 185 respectively.  The ammonium metal fluoride in solution may be hydrolysed to the hydrated metal oxide by the addition of ammonia solution, the former being removed by filtration and ammonium fluoride being recovered from the filtrate, or the ammonium fluoride concentration of the solution of ammonium metal fluoride may be increased and the resultant crystals of the ammonium metal fluoride separated by filtration and ammonium fluoride recovered from the filtrate.  Chemical machining may be accomplished by masking the metal article, except for the area to be removed, with a protective coating after which the article is immersed and the unprotected areas dissolved at a controlled rate in neutral ammonium fluoride solution.